Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$92.85	6.436%	$98.8258	$98.83	$98.85	$98.80
Purchase #2	$191.76	12.383%	$215.5056	$215.51	$215.50	$215.50
Purchase #3	$210.55	12.434%	$236.7298	$236.73	$236.75	$236.70
Purchase #4	$55.45	7.285%	$59.4895	$59.49	$59.50	$59.50
Purchase #5	$220.27	4.205%	$229.5324	$229.53	$229.55	$229.50
Purchase #6	$34.70	7.824%	$37.4149	$37.41	$37.40	$37.40
Purchase #7	$70.31	13.227%	$79.6099	$79.61	$79.60	$79.60
7 purchase totals =	$875.89		$957.1079	$957.11	$957.15	$957.00